1. Field of the Invention
This invention relates generally to systems for displaying graphics images on a raster display screen and, more particularly, to graphics display systems which allow the operator to interact to modify or change the displayed images. This invention more particularly relates to methods and apparatus implementing an operator selection or picking process in a pipeline graphics system.
2. Background of the Invention
Graphics display systems for generating and displaying two and three dimensional graphics objects have become increasingly complex. Graphics system operators demand increasingly rapid system response times for increasingly complex graphics objects. Graphics display system technology, in turn, has evolved to meet the combined demands for complex images and rapid response time.
Graphics display system performance has been improved through the use of pipelined graphics processors. In a pipelined graphics system a number of processors divide the work of drawing a graphics image. The pipeline processors are organized so that one of the processors can begin processing the next drawing order before second and subsequent processors have completed the processing of prior orders. In this way, each of the processors is active during each processing cycle though on different parts of the drawing order. The order to create a particular image is passed down the pipeline from the first processor through subsequent processors until the final image is created in video pixel memory. The simultaneous processing of multiple graphics orders greatly increases the overall operating speed of the machine. The number of pipeline stages in a complex graphics system can exceed 100 level.
An example of such a system is shown in FIG. 1. Graphics control processor 100 accesses the system memory 102 to receive graphics orders. Graphics control processor 100 translates the orders into specific graphics commands which are passed to the graphics pipeline processors 104. Several graphics processors may be present in the graphics pipeline to perform functions such as translation, rotation, scaling, mapping, and clipping of the graphics object. In addition, the pipeline processors are responsible for drawing the final image that is placed in the video pixel memory 106 for subsequent display on graphics display monitor 108. A graphics display system also typically contains pick detect logic 110 which is used to detect an object selected by the system operator.